This invention relates to copolymeric crosslinked materials, articles incorporating them and methods of using them.
Silicones are ubiquitous in commercially available manufactured goods as well as high-technology applications. Common forms of silicones include oils, rubbers, resins, and hard solids. The broad range of beneficial properties of this class of materials has led to their immense technological and commercial importance. Examples of such properties include their low dielectric constant, thermomechanical stability, biocompatability, optical transparency, highly variable mechanical hardness from rigid to elastic, controllable porosity, and a wide range of available interfacial properties from hydrophilic to extremely hydrophobic that depend on the type and concentration of organic modification. Moreover, the members of this class of materials may be synthesized via low temperature chemical processes that allow the incorporation of organic components and molecular additives.
Silicones are formed by converting silicone pre-polymers and resins into polymers, gels, and glasses by forming intermolecular siloxane (xe2x80x94Sixe2x80x94Oxe2x80x94Sixe2x80x94) and/or carbon-carbon covalent bonds via crosslinking processes (also termed xe2x80x9cvulcanizationxe2x80x9d or xe2x80x9ccuringxe2x80x9d) [1,2]. Typically, the new chemical bonds are introduced by the addition of peroxide compounds under ambient or elevated temperature, by reaction with or catalysis by organometallic or organosilicon compounds, by exposure to high energy radiation, or by condensative polymerization of residual silanol groups (xe2x80x94Sixe2x80x94OH) with another silanol or silane (xe2x80x94Sixe2x80x94H).
Silicones have a number of characteristics that limit their use. One limitation of covalently crosslinked silicones is that the crosslinks are not reformed if broken by thermal or mechanical forces. Another is that silicone materials often exhibit a very low fracture toughness (or xe2x80x9ctear-resistancexe2x80x9d). A few instances of improving toughness in silicones have been demonstrated by chemically bonding organic polymer segments with polysiloxane segments to form alternating block copolymers [5-9]. Lastly, silicones are not generally processable after they are completely cured and instead take a permanent shape.
Biological material systems have long been studied for their extraordinary mechanical properties, including combinations of adhesion, strength, flexibility, fatigue resistance, and self-repair that remain unmatched in synthetic systems [10-18, 37]. So-called secondary structures are essential for providing the characteristic high-toughness properties of natural structural proteins such as keratins, collagens, silk, and lustrin. In each of these, self-assembled arrays of inter- and intramolecular hydrogen bonds act in concert to stabilize the material [14-18]. These secondary structures are often assembled together as components of complex hierarchically ordered materials. To a large extent, however, it is the ability of the secondary structures to be reversibly disassembled and re-formed that is responsible for the toughness of natural fibers and adhesives as well as being a key to their observed self-repair and resistance to fatigue stresses.
There is a need in the art for self-healing materials, and for devices, compositions and articles of manufacture useful in such methods.
The present invention combines the impressive characteristics of biological structural materials into technologically useful silicon-based polymeric material systems. A crosslinked copolymeric material comprising an optionally substituted silicon component and a plurality of noncovalent crosslinking components is provided. The silicon components are attached to a plurality of crosslinking components which crosslink the material with a plurality of intermediate strength bonds which components on other silicon components. The crosslinking components may be end-linked to the end of linear silicon components, may be side-grafted to the silicon component, or both. The silicon components comprise a polymer selected from silicates, siloxanes, and silsesquioxanes, and mixtures and combinations thereof. The crosslinking components comprise polymeric domains which form intermediate-strength crosslinks by virtue of hydrogen and/or ionic bonding, either intramolecularly or intermolecularly. The intermediate-strength crosslinks provide a good overall toughness to the material, while allowing for self-healing by reformation of crosslinks after a stress incidence. Additionally, the intermediate-strength crosslinks allow for recasting of the material. Methods of recasting the material thus provided are also described, as are articles of manufacture incorporating the material.
Such energy-dispersive, self-healing materials can be incorporated in a variety of existing silicone applications as well as new applications, including as advanced marine or biomedical adhesives, as sealant compounds or components, in lightweight armors, as wear-resistant fibers, in protective and/or decorative coatings, in thermal insulators, in optical and electronic components, in satellites, and in biomedical devices.